Luther’s Reformation resulted in a religious but also a political schism within the Holy Roman Empire. Defying imperial rule, between December 1530 and February 1531 Charles V’s opponents joined forces to found the Schmalkaldic League in the small German city of Schmalkalden.

Imperial propaganda presented the campaign against the Schmalkaldic League as a political rather than a religious conflict, intended to punish those who had risen up against their lawful master, including John Frederick, Elector of Saxony and Philip the Magnanimous, Landgrave of Hesse. In fact, notable Lutherans such as Maurice of Saxony and the Princes of Wittelsbach and Cleves supported Charles and his brother, the Archduke Ferdinand (the future Emperor), whose armies were largely made up of Protestant troops.